The present invention relates to a method of producing compression molded coal having bulk density of 1.0 wet Ton/m.sup.3 or more.
Hithertofore the chamber type coke ovens has widely been utilized for a method of the so-called top charge wherein coking coal is charged into the oven chambers through charging holes in the oven ceiling. Recently attempts are being made to increase the bulk density of the raw material coal to be charged into the oven from the top so as to improve coking properties, productivity, and to expand selection range out of the raw material coal. To this end, a process has been developed in which the raw material coal will be formed into briquettes prior to charging in a forming machine and 30% of the produced briquettes are mixed with the charging coal to increase the bulk density by 10%. The method of charging a briquette blended coal as above mentioned is intended to increase the strength of the coke by increasing the bulk density of the coal to be charged. The attained bulk density is, however, in the order of 0.8 dry ton/m.sup.3 which seems to be considerably lower compared to 1.0 wet ton/m.sup.3 or more (0.91 dry ton/m.sup.3 in case that the water content is 9%), which may be provided in accordance with the present invention.
In the meantime, such a method of compacting the coal has been put in practice as raw material coal is vertically introduced in layers into a stamping box which is substantially same in size with a coke oven chamber, and is compacted to a coal cake in the stamping box by a high frequency drop hammer unit. It is described that the stamped bulk density having more than 1.1 wet ton/m.sup.3 or more than 1.2 wet ton/m.sup.3 may be obtained according to this method (Japanese Patent laid open No. Sho-53-25602, Germany Patent application No. P 26 29 122.5). However, this process results in such problems as the time required for compaction will take along and vibration, and noise will be generated due to shock of the stamping action.
Furthermore, an arrangement to produce press molded coal cake by means of press has been proposed since many years. In this arrangement, however, the molding box of press and the relative press devices have to be prepared corresponding to the size of the required compression molded coal. To achieve this end, the stroke of the hydraulic cylinder has to be long and the pressing area has to be adequately large. Besides, the entire molding box has to be strengthened so as to resist the pressing force, to thereby require huge compressing devices and accordingly to increase of the cost. In addition to the above problem, a separate step will be required for taking the compression molded coal out of the molding box and due to this additional work, the time of compression molding operation will have to be longer.
The object of the present invention is to provide a method of producing compression molded coal cakes to be charged into the chamber of the coke oven by eliminating the drawbacks described above and also increasing the strength of the coke, whereby expanding the range out of which the raw material coal may be selected, improving the productivity and eliminating the unfavorable work at the top of the coke oven and air pollution due to generation of dust.
The object of the present invention may be accomplished by the inventive method of producing an endless compressed molded coal cake, having a bulk density of 1.0 wet ton/m.sup.3 or more, the method comprising the repetition of the steps of leaving around the outlet of the molding box the molded coal compressed already, charging raw material coal into the molding box, carrying out the compression molding of the raw material coal charged into the molding box, combining the fresh compression molded coal with the already compression molded coal during compression, and pushing a part of combined compressing molded coal out of the molding box.
Normally when the raw material coal particles are pressurized in a molding box, frictional force will be generated over the wall of the molding box. The same phenomenon may be seen when the already compression molded coal staying inside the molding box is pushed out of the box. Therefore, it is necessary to apply pressing force capable of overcoming the frictional resistance of already compression molded coal in order to push out the molded coal. According to the present invention, the frictional resistance which has to be overcome at the time of pushing out the molded coal may be used as the supporting force for the fresh charged raw material coal to be compressing molded, and after completion of compression, pressing force capable of overcoming the above mentioned frictional force will be applied to push the compression moded coal out of the molding box.
In other words, the defined friction force may so easily be obtained by selecting the size, that is, actual length of the compression molded coal which is still remaining in the molding box. When fresh raw material coal is charged into the space defined between the pressing plate and the preceding compression molded coal, a part of which is remained in the molding box, and is compression molded by advancing said pressing plate, the molded coal which is formed in succession will have a bulk density of 1.0 wet ton/m.sup.3 or more. During pressing operation, the coal which has already been compression molded before will be pushed out of the molding box. The present invention is capable of continuously producing an endless cake of compression molded coal by repeating the above operation in series intermittently.
In the case of the so-called coal cake charging method wherein the compression molded coal is to be charged from the door side of the oven chamber, no smooth charging of the molded coal may be anticipated due to breakage at the time of charging unless the bulk density of the molded coal will be more than 1.0 wet ton/m.sup.3. In the worst case, such collapse of the molded coal will be so considerable that the door may not be fastened, or the compression molded coal may catch fire resulting in a serious troubles of the operation. For this reason, it is necessary for the compression molded coal to have a bulk density of more than 1.0 wet ton/m.sup.3, preferably 1.15 wet ton/m.sup.3 or more. From the foregoing description, according to the present invention, such a pressure will be selected as to enable the raw material coal to be compressed by said pressure to be made into molded coal having a bulk density of 1.0 wet ton/m.sup.3 or more and to be combined with the preceding molded coal which have already be compression molded.
That is, when the raw material coal particles will be pressureized with a pressure of P kg/cm.sup.2, pressure ps kg/cm.sup.2 will be generated over the walls of the molding box and frictional force .mu.Ps kg/cm.sup.2 (.mu.stands for coefficiency of friction) will be produced. FIG. 2 illustrates the relation between the pressure -P over the thickness dH of the particles layer and the frictional force .mu.Ps. If the self gravity of the raw material coal will be neglected, for it is small compared to the pressure, the friction force .mu.Ps can be understood as the function of the thickness H of the layer of the raw material coal, the area F to be pressureized and the peripheral length U of the metallic mold. EQU Ps=f (P, H. F, U) . . . (1)
When the oven to be subject to coal cake charge is selected, the peripheral length U of the metal mold and the area F to be pressurized may be determined by the dimension of the ovens in question. Since the compression molded coal in a position of the layer thickness H generates the friction force .mu.Ps against the upward pressure in the molding box, the supporting force for the already compression molded coal which is still remaining in the molding box owing to the above friction force .mu.Ps may be determined. As described above, if the pressure P and the thickness H of the coal layer are given, the friction force .mu.Ps can be determined whereby the quantity or size of the preceding compression molded coal which has to be retained in the molding box may be determined in accordance with the above equation (1). The inventor of the present invention has an experience in which the pressure required for the pressing plate to obtain the compression molded coal having a bulk density of 1.0 wet ton/m.sup.3 in the molding box having the sectional area of 350 mm.times.1.000 mm will be in the order of 50 kg/cm.sup.2. In this manner, by leaving the preceding compression molded coal having a bulk density of 1.0 wet ton/m.sup.3 or more at the outlet of the molding box, when the raw material coal are freshly charged and pressed in the space defined between the pressing plate and said preceding compression molded coal in the molding box, said preceding compression molded coal will serve as the supporting force for the freshly charged coal against compression, whereby the freshly charged coal may be compressed to the maximum extent due to the friction resistance generated immediately before and after the pushing out operation for the molded coal. Thus, by suitably selecting the thickness of the layer of the preceding compression molded coal which have to be retained in the molding box and the quantity or the thickness of the layer of the freshly charged coal, said pressing plate apply with the pressure (50 kg/cm.sup.2) necessary for obtaining the compression molded coal having a bulk density of 1.0 wet ton/m.sup.3 or more or preferably a pressure (100 kg/cm.sup.2) necessary for attaining the compression molded coal having a bulk density of 1.15 wet ton/m.sup.3 or more may be applied by said pressing plate.
Furthermore, so long as the pressure P exceeding the balanced condition with the friction force .mu.Ps will be continuously applied, the compression molded coal produced already in the molding box may be continuously pushed out of the box, while the intermittent operation conducted successively may permit an endless chain of the compression molded coal.
By constructing the molded coal in the above mentioned manner, the molding box may not necessarily extend along the entire length of the block of molded coal to be produced but should extend to the extent sufficient for a unit of operation, that is, the length necessary for the compression part for charging, compression and pushing-out of the material coal and the resistance generating part. Thus the molding box is made in a compact design. Furthermore, the present invention permits the molding device to be of the smallest possible design and exhibits an excellent characteristic in the economical aspect in that the molding box will not be restricted in the sectional size of the compression molded coal to be produced and may be adapted to the dimension of the charged block as well as the compression surface will be provided where the pressurizing area is smallest. In addition, in case of the present invention, there will be no limitation in respect of the direction in which the compression molded coal is to be pushed out. Accordingly any of the directions including transverse, longitudinal and slanting ones may be adopted. Besides, there is also no restriction in terms of the attitude of the compression molded coal to be treated, that is, the shorter side of the rectangular section of the molded coal may be put lowerside, the longer side thereof may be put lowerside or the rectangular section may be slanted.